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How to Optimize Your Js-Based Progressive Web Apps SEO FOR PWA HOW TO OPTIMIZE YOUR JS-BASED PROGRESSIVE WEB APPS REPORT BY Introduction The goal of this whitepaper is to help you better understand how search engines perceive JS-powered sites, what their limitations are, and how the potential threats can be prevented to make your PWA a great product in the world of mobile-first indexing where great user experiences take the lead. Firstly, we introduce the advantages of Progressive Web Apps over native apps and what allows them to deliver engaging and fast user experiences. The process of crawling, rendering, and indexing JS-rich sites by Google is explained, alongside the limitations from its use of the dated version of the Chrome browser to render pages, and the extensive resources needed to execute JavaScript. The general guidelines to mitigate the most important issues related to not only PWAs, but generally any sites built around the Single Page App model regardless of specific frameworks, AUTHOR as these problems are common across the board, are also included. Lastly, we outline Paulina Piotrowicz JS rendering solutions that SEO Specialist can be used to make any Elephate JS-powered site more SEO- friendly, just like any other HTML site. 2 SEO for PWA Introduction to Progressive Web Apps Progressive Web Apps provide engaging, PWAs means the layout is automatically native app-like experiences, without the adjusted to fit the screen resolution - be it excess of local device storage. Thanks to a mobile, tablet or desktop. Great examples set of APIs and service workers, PWAs are of efficient PWAs includeAlibaba.com , reliable on flabby networks or evenoffline , Lancôme or Starbucks. come with payment mechanisms, and Progressive Web Apps are mobile-first push notifications tore-engage previous oriented and extremely lightweight website visitors. compared to native apps, providing the PWAs are more accessible than standard same level of interactivity. After the initial native apps - the distribution model page renders, they act just like a normal doesn’t require users to go to their OS store Single Page Application (SPA), where the to download the app. On both Android and body contents are dynamically loaded with iOS, all a user needs to access a PWA is a JavaScript. Even with the subsequent JS browser. Once added to the homescreen, chunks transferred to refresh the content, a PWA features a permanent icon shortcut. the overall payloads of PWAs are unlikely to Native-like apps that live on the web are exceed the cost of an upfront download of crawlable and indexable, enabling the a native app. In the case of Pinterest’s PWA, launch and maintenance of one product the compressed payload of the app was that not only provides outstanding user only 150 KB compared to the staggering experiences on all devices but also satisfies 56 MB of a native app required for the same the crawlers. The responsive design of experience on Apple devices. 3 SEO for PWA GREY - medium value and medium churn risk Comparing the PWA to the native apps 60 56 MB 45 30 15 150KB home 9.6 MB feed load 0 Android iOS PWA Source: Addy Osmani - A Pinterest Progressive Web App Performance Case Study Mobile sites need to load fast and their affected. With mobile page loading speed perceived load speed must feel fast - 53% now a ranking factor, if the JS-powered percent of visits are abandoned if a mobile web app properly mitigates all crawling site takes longer than 3 seconds to load. and indexability issues, its organic visibility PWAs utilize placeholders ready to be filled can benefit from an outstanding user with downloaded content, giving users experience and an improved perceived the sense that the app is loading instantly. page load. Even if Googlebot itself is not Thanks to the Service Workers responsible able to directly benefit from the heavy for heavily caching the app shell containing client-side caching, it’s able to track real- all the main JS and CSS, users are gratified world page performance as perceived with the snappy interactiveness on the by of your actual app users. Chrome repeated visits. User Experience Report (CrUX) gathers JavaScript-based apps can be rendered in pagespeed statistics from Chrome browser the user browser (client-side rendering - users, and it’s safe to assume that those CSR) or rendered fully on the server (server metrics are then factored in when search side rendered - SSR), with mixed solutions rankings are computed. in-between. We talk about these techniques in detail later on. Depending on the rendering type you choose, SEO-friendliness, loading speed and the performance of the app will be 4 SEO for PWA While it was a great step towards Current state a JS-dominated web, and it’s been 3 years since the initial announcement, there are of JavaScript still notable obstacles in maximizing the visibility potential of apps based on pure JS, & SEO where literally no content is visible before the scripts are executed. John Mueller of Google admitted there are Introduction some JS-powered sites where Googlebot will be able to handle client-side JS (“some” As of July 2018, the only search engine able being the keyword here). It indicates to efficiently parse and execute JavaScript Google will struggle in all other cases: is Google. Although the other bigger player on the market, Bing, is capable of rendering JavaScript, it doesn’t do it at scale. It was back in 2015 when Google first announced that they are generally able to render and understand JS-powered websites just like modern browsers: Times have changed. Today, as long as you’re not blocking Googlebot from crawling your JavaScript or CSS files, we are generally able to render and understand your web pages like modern browsers. To reflect this improvement, we recently updated our technical Webmaster Guidelines to recommend against disallowing Googlebot from crawling your site’s CSS or JS files. Source: https://webmasters.googleblog.com 5 SEO for PWA Expensive JS execution JS is heavy on CPU, time-consuming, and slower to parse than “raw” HTML. Because of limited CPU capabilities, according to a Web Apps Performance Study from Q4/16-Q1/17, JS parse times on mobile devices can be up to 36% longer than on desktop. The size of JS chunks, code quality, and complexity (not every 100 KB load of JavaScript will be equal in terms of the resources required to parse and compile) can noticeably affect battery usage, especially on low-end smartphones with both limited battery life and weaker processors. Longer JS execution times forced on the user’s device delay the first paint of the “hero” content that the user is keen to see on the screen. This will be visible in metrics such as Time to First Paint and First Contentful Paint that aim to measure how quickly content is served to users - and both are part of the CrUX reports. Two waves of indexing JavaScript-rich websites In the case of heavy JS-dependant sites, compiles and executes all JS scripts, Googlebot crawls and then queues only including fetching data from databases content and links discovered upon the first and external APIs. At this point, Caffeine crawl of the server-side rendered response can index the JS-generated body contents. to be immediately indexed. Rendering the All new links discovered by WRS are then remaining client-side JS and extracting queued to be crawled by Googlebot and JS-injected links is deferred until Google’s the process repeats. processing resources become available. Waves of Indexing for JS-powered websites Algorithms are used to determine whether a given external resource is essential for Instant, first CRAWL wave of a valid render of the page. If its algorithm indexing decides it’s not crucial for rendering As rendering purposes, the file won’t be fetched at this resources become available time. New INDEX links to be When processing resources become crawled available, Web Rendering Service (WRS) - part of the Caffeine indexer - parses, Second wave RENDER of indexing Source: Deliver search-friendly JavaScript-powered websites 6 SEO for PWA (Google I/O ‚18) Between the two waves of indexing, some key page elements crucial for indexing (such as meta tags or rel canonical) can be missed by Googlebot if they are not included in the initial server response, or the two versions can be sending mixed signals to Google on how it’s supposed to treat your pages. If your source code uses meta robots tag “index”, clearly telling Googlebot the page is indexable, but JS scripts change it to “noindex”, the page will initially be indexed anyway. To see the noindex directive (and consequently de-index the page), Google will need to wait until WRS takes over and renders the full Document Model Object (DOM). Dynamic HTML in DOM is what the browser formed after it received the static HTML document and then fetched all the linked assets, including CSS and JS - so DOM includes your JS-generated content. Unfortunately, for some less-important pages, it can be days until the second wave of crawling kicks in after the initial indexing. Between those two events, the page may as well be found in the search results. Limitations of Googlebot & the Web Rendering Service The WRS responsible for rendering is in fact • Session data storage & cookies is a headless Chrome 41 browser. Released in cleared across page loads - Google 2015, it comes with certain limitations when wants to see pages just like any first-time compared to more modern browsers: user would • Service Workers are only partially • WRS does not support WebSocket supported for Googlebot (Chrome 41) protocol • There is no guarantee all your JS files will • IndexedDB and WebSQL interfaces are be downloaded upon the initial crawl of disabled your web page • Chrome 41 supports ES5 syntax only (limited capabilities in the newer The general rule of thumb is that if your JS versions) web pages are properly rendered both in • Googlebot and WRS support only Chrome 41 and Search Console using the HTTP/1.x and FTP, with or without TLS Fetch as Google tool, the engine should • All user permission requests are technically be able to correctly see the automatically denied pages as well.
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